1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and to a method of manufacturing such a magnetic head.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction orthogonal to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
Typically, magnetic heads for perpendicular magnetic recording have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter referred to an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate, as is the case with magnetic heads for longitudinal magnetic recording. The write head incorporates a pole layer that produces a magnetic field in the direction orthogonal to the surface of the recording medium. The pole layer includes, for example, a track width defining portion having an end located in a medium facing surface that faces toward the recording medium, and a wide portion that is coupled to the other end of the track width defining portion and that is greater in width than the track width defining portion. The track width defining portion has a nearly uniform width.
For the perpendicular magnetic recording system, it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in write characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, if the track width is reduced, the writing characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, suffer degradation. It is therefore required to achieve better write characteristics with decreasing track width. Here, the length of the track width defining portion taken in the direction orthogonal to the medium facing surface is called a neck height. The smaller the neck height, the better is the overwrite property.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider is designed to slightly fly over the surface of the recording medium by means of the airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive, the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system that exhibits a better capability of writing on a recording medium than the longitudinal magnetic recording system, in particular, if the skew mentioned above occurs, there arise problems, such as a phenomenon in which, when data is written on a certain track, data stored on a track adjacent thereto is erased (that is hereinafter called adjacent track erasing), or unwanted writing between two adjacent tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between two adjacent tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
As one of techniques for preventing the problems resulting from the skew described above, there is known a technique in which the end face of the track width defining portion located in the medium facing surface is formed into such a shape that the side located backward along the direction of travel of the recording medium (that is, the side located closer to the air inflow end of the slider) is shorter than the opposite side, as disclosed in U.S. Pat. No. 6,710,973 and JP 2003-203311A, for example. For magnetic heads, typically, in the medium facing surface, the end farther from the substrate is located forward along the direction of travel of the recording medium (that is, located closer to the air outflow end of the slider). Therefore, the shape of the end face of the track width defining portion located in the medium facing surface mentioned above is such that the side closer to the substrate is shorter than the side farther from the substrate.
Consideration will now be given to a method of forming a pole layer in which the end face of the track width defining portion located in the medium facing surface has such a shape that the side closer to the substrate is shorter than the side farther from the substrate as described above. U.S. Pat. No. 6,710,973 discloses a method of forming a pole layer through the steps of etching an inorganic insulating film using a patterned resist as a mask to thereby form a groove in the inorganic insulating film; subsequently forming a stopper film; further forming a magnetic film; and flattening the top surface of the magnetic film. JP 2003-203311A discloses a method of forming a pole layer by etching a magnetic layer using a mask.
In the pole layer formed by the method disclosed in U.S. Pat. No. 6,710,973 or the method disclosed in JP 2003-203311A, a great part of the side surface of the pole layer along the entire perimeter of the pole layer is formed into a surface inclined with respect to the direction orthogonal to the top surface of the substrate. In the pole layer having such a shape, the cross-sectional area of the pole layer taken in the direction orthogonal to the direction in which magnetic flux flows is smaller, compared with a case in which the entire side surface of the pole layer is orthogonal to the top surface of the substrate. According to the pole layer having the above-described shape, it is impossible to allow magnetic flux of great magnitude to pass through a portion near the boundary between the track width defining portion and the wide portion, and as a result, write characteristics such as an overwrite property will be degraded. It is therefore inevitable to reduce the neck height of the pole layer having the above-described shape so as to suppress degradation of write characteristics.
It is difficult to precisely form a portion of the side surface of the pole layer near the boundary between the track width defining portion and the wide portion. It is therefore likely that the portion of the pole layer near the boundary between the track width defining portion and the wide portion has such a shape that the width gradually increases with increasing distance from the medium facing surface. As a result, if the neck height is reduced, it is difficult to precisely define the width of the track width defining portion located in the medium facing surface, that is, the track width.
Because of these factors, it has been conventionally difficult to implement a pole layer that enables both of precise definition of the track width and an improvement in write characteristics.